The quality which can be obtained for a hardmetal grade depends considerably on the nature of the starting powder materials which are formed into a shaped hardmetal body by pressing and sintering. The chemical-metallurgical composition in this case is just as significant as the morphology and structure of the powder, and therefore the dressing of the powder before press compaction and sintering.
In recent years, efforts for manufacturing improved hardmetal qualities were concentrated primarily on the attainment of fine graininess and homogeneity of the hard materials in the hardmetal.
The metallic components in the hardmetal's carbide-hard material phase are tungsten or titanium, and small amounts of the refractory metals tantalum, niobium, molybdenum, vanadium, and chromium in the form of grain-stabilizing composite carbides.
In the long procedural sequence of ore dressing these metals, the processing steps, starting with the reduction of powdered metallic oxides or comparable compounds like ammonium metalates and metallic acids, up to the extraction of metal carbide, are essential for the later quality of hardmetal types, particularly in regard to their metallic structure.
Metal oxides, or comparable compounds familiar to a skilled person, are reduced to pure metal in one or more processing steps, and the metal is subsequently converted to metal carbide, usually in a separate processing step. In rare cases, reduction and carburization are also carried out in one common continuous process.
For metal oxide reduction in a solid-gas reaction, metal oxides are continuously led through a reduction furnace on carrier saggers in comparatively thin layers. Reduction in a rotary kiln and in a fluidized bed are equally well known.
Conventional processes for carbide production are the intimate mixing of powdered metal, tungsten powdered metal for example, with carbon (carbon black particles) and subsequent reaction in a carburizing furnace.
Besides powder quality, the economics of production play an important role in commercial production. It is determined by the price of the device corresponding to the process's complexity, by the amounts of energy and reaction gas used for each reaction unit, and, above all, by the factor of production time.
The reaction or processing times of the powder in each of the cited devices, without exception, lie in the range of hours, 1 to 2 hours in the most favorable case, reaction times of 15 to 20 hours in the most unfavorable cases.
Besides the chemical steps of reduction and carburization, procedural steps like grinding and mixing events, which as a rule again take many hours, belong to the complete production. Additionally, the processes for dressing powder, like the granulation of powders by spray drying for example, are largely unavoidable in the hardmetal industry.
New processes, in which conventional reduction and carburization, including special powder preparation and dressing procedures, run simultaneously or at a compelling pace, were developed in connection with the demand for submicron and nanophase powders for hardmetal feed materials.
WO 91/07244 entitled "Spruhumwandlungsproze.beta. fur die Herstellung von Nanophasen-Verbundpulver" and WO 95/04703 entitled "Verfahren zur Herstellung von Submikrometer-Karbiden, Submikrometer-Mischkristallkarbiden und daraus entstehende Materiallen" are representative for these types of processes and devices used for them, whereby the latter patent document makes a reference to U.S. Pat. No. 5,110,565 in which a reactor is described as it is used for carrying out the process in accordance with the WO application.
The high manufacturing costs and costs for the devices are disadvantageous in these processes. In spite of some reductions relative to the known state of technology at the time, the reaction times, as a whole, for the unavoidable procedural steps to be carried out are still on the order of one to several hours, and are therefore a substantial cost factor. These processes are therefore uneconomical, as a whole, particularly as regards the achievement of powder fine graininess in comparison with the standard processes described farther toward the beginning.